I read once where he would never have been a saint if he hadn't been martyred. Which reminds me of of Amy Welborn's comment on her home page, "She could never be a saint, but she thought she could be a martyr if they killed her quick." (This quote is what endeared Amy to me - one has to love such humility.)
I think Becket was Richard Burton's best role. St. Thomas was very worldly, athletic, finely educated, and possessed exquisite taste. Amidst all the temptations of court it is said he remained virtuous and chaste. Always a just man, even though the king's best friend.
He died opposing the State, murdered in his Cathedral at vespers. After his death his piety and asceticism were soon found out, he had worn a hairshirt, and privately lived a penitential life with minimal comforts. Actually, I think he would have been a saint regardless of the martyrdom.
Henry VIII dismantled his shrine and his relics were lost, undergoing a posthumous martyrdom of sorts at the hands of another king I'd say.
Catholic Online has a good biography on the saint while Fr. Nicholas has an interesting post on the feastday as observed in the UK.
St. Thomas Becket brings to mind a similar martyr - I wonder if Archbishop Oscar Romero will ever be canonized? He does have the title, "Servant of God".